The effect of the choice of crystallisation solvent on the stoichiometry of salts formed by a spherical base (adamantylamine, pK_a = 10.7) and a planar triprotic acid (trinitrophloroglucinol, pK_a1 < 0, pK_a2 = 2.9, pK_a3 = 6.5) was studied by dissolving a 3 : 1 mixture of the base and the acid in a series of 13 solvents. This has resulted in isolation of 10 distinct phases: a solvent free 1 : 1 salt, and nine solvates – two of 2 : 1 salts, one of a 5 : 2 salt and six solvates of 3 : 1 salts. With the exception of one 2 : 1 salt, all structures were layered with a hydrogen bonded network comprising anions, –NH³⁺ groups of the cations, and oxygen atoms or hydroxyl groups of the solvent molecules (if present) in the middle of the layer, and the hydrophobic adamantyl groups on either side. In solvates of the 3 : 1 salts with alcohols, these adamantyl groups form arrays of pentagons with remaining space filled by solvent molecules. This was observed only with smaller alcohols (MeOH, EtOH, trifluoroethanol and propanol) as well as water molecules, while larger alcohols lead to formation of the solvent free 1 : 1 salt. The structures of the 1 : 1 and 2 : 1 salts were found to be similar to those of equivalent adamantylammonium picrate and styphnate.

Hybrid metal-organic compounds as relatively new and prosperous magnetoelectric multiferroics provide opportunities to improve the polarization, magnetization and magneto-electric coupling at the same time, which usually have some limitations in the common type-I and type-II multiferroics. In this work we investigate the crystal of guanidinium copper (II) formate [C(NH${}_2$)${}_3$]Cu(HCOO)${}_3$ and give novel insights concerning the structure, magnetic, electric and magneto-electric behaviour of this interesting material. Detailed analysis of crystal structure at 100 K is given. Magnetization points to the copper (II) formate spin-chain phase that becomes ordered below 4.6 K into the canted antiferromagnetic (AFM) state, as a result of super-exchange interaction over different formate bridges. The performed ab-initio colinear density functional theory (DFT) calculations confirm the AFM-like ground state as a first approximation and explain the coupling of spin-chains into the AFM ordered lattice. In versatile measurements of magnetization of a crystal, including transverse component besides the longitudinal one, very large anisotropy is found that might originate from canting of the coordination octahedra around copper (II) in cooperation with the canted AFM order. With cooling down in zero fields the generation of spontaneous polarization is observed step-wise below 270 K and 210 K and the effect of magnetic field on its value is observed also in the paramagnetic phase. Measured polarization is somewhat smaller than the DFT value in the c-direction, possibly due to twin domains present in the crystal. The considerable magneto-electric coupling below the magnetic transition temperature is measured with different orientations of the crystal in magnetic field, giving altogether the new light onto the magneto-electric effect in this material.

Calcium phosphates (CaPs) composites with silver nanoparticles (AgNPs) attract attention as a possible alternative to conventional approaches to combating orthopedic implant-associated infections. Although precipitation of calcium phosphates at room temperatures was pointed out as an advantageous method for the preparation of various CaP-based biomaterials, to the best of our knowledge, no such study exists for the preparation of CaPs/AgNP composites. Motivated by this lack of data in this study we investigated the influence of AgNPs stabilized with citrate (cit-AgNPs), poly(vinylpyrrolidone) (PVP-AgNPs), and sodium bis(2-ethylhexyl) sulfosuccinate (AOT-AgNPs) in the concentration range 5–25 mg dm⁻³ on the precipitation of CaPs. The first solid phase to precipitate in the investigated precipitation system was amorphous calcium phosphate (ACP). The effect of AgNPs on ACP stability was significant only in the presence of the highest concentration of AOT-AgNPs. However, in all precipitation systems containing AgNPs, the morphology of ACP was affected, as gel-like precipitates formed in addition to the typical chain-like aggregates of spherical particles. The exact effect depended on the type of AgNPs. After 60 min of reaction time, a mixture of calcium-deficient hydroxyapatite (CaDHA) and a smaller amount of octacalcium phosphate (OCP) formed. PXRD and EPR data point out that the amount of formed OCP decreases with increasing AgNPs concentration. The obtained results showed that AgNPs can modify the precipitation of CaPs and that CaPs properties can be fine-tuned by the choice of stabilizing agent. Furthermore, it was shown that precipitation can be used as a simple and fast method for CaP/AgNPs composites preparation which is of special interest for biomaterials preparation.

Competitive milling was successfully employed to determine the relative affinity of copper(II) ions towards selected L-amino acids (Asn, Gln, His, Phe, Pro, and Trp). Although Cu(II) ions readily form complexes with all the investigated acids, only L-Trp is selectively bound from its solid (binary) mixtures [in the form of Cu(Trp)₂]. For the investigated reactions, solid-state milling proved to be superior to solution-based methods as it avoids unwanted competition and solubility problems while opening a simple route towards ternary coordination compounds (otherwise hard to obtain from solution).

Background and purpose: To discover novel compounds active against sensitive and resistant bacterial strains, a series of novel azithromycin-thiosemicarbazone conjugates, the macrozones, have been syn­the­sized and their biological activity evaluated with corresponding (quantitative) structure-activity relationship ((Q)SAR) analyses conducted. Experimental approach: A systematic variation of thiosemicarbazone side-chains and coupling at positions 4''-, 3-, and 9a of the azithromycin scaffold has resulted in a novel class of bacterial ribosome inhibitors. Key results: Compared to azithromycin, the activity of 4''-macrozones has shown the greatest improvements against efflux-resistant S. pneumoniae and S. aureus, as well as very good activity of 4'' derivatives against E. faecalis. QSAR calculations indicate that the antibacterial activity of macrozones is primarily determined by the position of the thiosemicarbazone side chain. Among the conjugated derivatives, the 4''-substituted macrozones exhibit the highest overall activity against a range of sensitive and efflux-resistant Gram-positive bacteria, as well as against Gram-negative E. coli strains, while those substituted at 9a- and 3- positions are found to be less potent. The antibacterial activity of macrozones is favourably influenced by larger fractions of their cationic and zwitterionic forms, their capacity for hydrogen bond formation, and the extension of p-electron delocalization involving the thiosemicarbazone moiety. Conclusion: The results obtained provide a sound basis for guiding further medicinal chemistry efforts toward the discovery of more potent macrolide anti-infectives, with particular emphasis on resistant bacteria that pose a serious threat to human health.